Such paving screeds are known in practice. They are used in road construction to smooth and compact layers of pavement, for example made of asphalt. Paving screeds of various designs are used, for example, fixed-width screeds whose width is invariable, fixed-width screeds whose width may be modified by means of separate add-on components, as well as extendable screeds whose width may be variably modified with the aid of extending units. Here too, separate bolt-on extensions may also be attached. So-called side plates are attached to each of the outer ends of the screed, which prevent material in front of and under the screed from escaping to the sides.
The width of the entire screed, also referred to as operating width, is an important parameter, since it affects important regulating variables of the road finisher, for example, the material needed in front of the screed and, therefore, the output or the speed of the material delivery systems of the road finisher. Due to the increasing automation of the operation of road finishers, it is advantageous to in some way provide the various control systems with the width of the paving screed.
In conventional screeds this still occurs frequently by manual input. In extendable screeds, measuring systems are used which identify the sliding path of the screed extensions. In the simplest case, this involves scales with pointers. Once read, the value must be added to the width of the base screed and input into the control system. Other measuring systems identify the sliding path and provide this directly to the machine control system. The addition of the respective sliding path and the width of the base screed is then handled by the control system. However, such systems do not take into account potentially separately mounted bolt-on extensions such that when the latter are used, another input by the operator must be made.
Applicant's European patent application EP 2 239 374 A1 discloses a road finisher which may be upgraded with multiple auxiliary components. Said auxiliary components are equipped with wirelessly readable identification devices which can be read out by a reading device on the road finisher. Auxiliary components mentioned are, among others, extending units of extendable paving screeds as well as fixed bolt-on extensions. Also provided is a measurement of the distance between the reading device on the road finisher and the identification means mounted on the extending units or bolt-on extensions. It has turned out that this system has optimization potential. For one, both the extending units of extending screeds as well as all separate bolt-on extensions must be provided with identification means. For another, the plurality of identification means gives rise to a significant fault potential. For example, it is necessary in very long screeds which have multiple add-on components to process a large number of signals, which increases the susceptibility to failures. Moreover, it may happen that the signal of the outermost add-on component cannot be received by the reading unit due to limited range or to distortions. If the latter then receives a signal of an add-on component situated further inward, the system, unbeknownst to the operator, is then provided with a false operating screed width. In addition, problems may also arise in conjunction with asymmetrically widened screeds, since it then becomes difficult to determine which signal from an add-on component indicates the correct screed width.